Sensor node voltage clamping circuit and method

Abstract

A voltage clamping circuit includes a current source having a fixed current source and a variable current source and a variable resistor receiving current from the current source. The variable resistor varies its resistance in response to an environmental operating condition. The voltage clamping circuit also includes an amplifier configured to compare a sensor node voltage with a reference voltage, the sensor node voltage being in communication with the voltage drop across the variable resistor. The amplifier is configured and connected to provide a control output to control the variable current source to modify current output from the variable current source to at least in part prevent the sensor node voltage from exceeding a reference voltage when certain operating conditions are present.

1. A device including a system for recharging a battery at a port of the device comprising:
 a rechargeable battery; 
 a thermistor associated with the rechargeable battery, the thermistor operable to vary its resistance in response to temperature of the rechargeable battery; 
 a voltage clamping circuit in communication with the thermistor, the voltage clamping circuit comprising:
 a current source comprising a fixed current source and a variable current source, the current source configured to be in communication with the thermistor when the rechargeable battery is connected to the port; 
 an amplifier configured to compare a sensor node voltage in communication with a voltage drop across the thermistor to a middle reference voltage between a low reference voltage indicative of the temperature of the rechargeable battery and a high reference voltage indicative of the rechargeable battery's being removed from the port, the amplifier configured and connected to provide a control output to control the variable current source to modify a current output from the variable current source to at least in part prevent the sensor node voltage from exceeding the middle reference voltage when the rechargeable battery is connected to the port. 
 
 
     
     
       2. The device of  claim 1  wherein the voltage clamping circuit further comprises:
 a first comparator configured to compare the sensor node voltage in communication with the voltage drop across the thermistor to the low reference voltage indicative of the temperature of the rechargeable battery. 
 
     
     
       3. The device of  claim 1  wherein the voltage clamping circuit further comprises:
 a second comparator configured to compare the sensor node voltage in communication with the voltage drop across the thermistor to the high reference voltage indicative of the rechargeable battery's being removed from the port. 
 
     
     
       4. The device of  claim 1  wherein the voltage clamping circuit further comprises:
 a first comparator configured to compare the sensor node voltage in communication with the voltage drop across the thermistor to the low reference voltage indicative of the temperature of the rechargeable battery; 
 a second comparator configured to compare the sensor node voltage in communication with the voltage drop across the thermistor to the high reference voltage indicative of the rechargeable battery's being removed from the port; 
 a digital element configured to accept a first comparator output from the first comparator and a second comparator output from the second comparator and to provide an operate output signal to the device when the first comparator output indicates that the sensor node voltage is less than a first reference voltage in indication that the rechargeable battery is not too cold to be recharged or when the second comparator output indicates that the sensor node voltage is greater than a second reference voltage in indication that the rechargeable battery has been removed from the port. 
 
     
     
       5. The device of  claim 1  wherein the voltage clamping circuit further comprises:
 a first comparator configured to compare the sensor node voltage in communication with the voltage drop across the thermistor to the low reference voltage indicative of the temperature of the rechargeable battery; 
 a second comparator configured to compare the sensor node voltage in communication with the voltage drop across the thermistor to the high reference voltage indicative of the rechargeable battery's being removed from the port; 
 a digital element configured to accept a first comparator output from the first comparator and a second comparator output from the second comparator and to provide a non-operable output signal to the device when the first comparator output indicates that the sensor node voltage is greater than a first reference voltage in indication that the rechargeable battery is too cold to be recharged and when the second comparator output indicates that the sensor node voltage is less than a second reference voltage in indication that the rechargeable battery is connected to the port. 
 
     
     
       6. The device of  claim 1  wherein the amplifier and the variable current source are configured to reduce the current output from the variable current source to prevent at least in part the sensor voltage from exceeding a third reference voltage when the rechargeable battery is connected to the port. 
     
     
       7. The device of  claim 1  wherein the sensor node voltage approaches a device operating voltage that is higher than a second reference voltage when the rechargeable battery is removed from the port of the device. 
     
     
       8. The device of  claim 1  wherein the fixed current source continues providing current after the current output from the variable current source is reduced to approximately zero such that when a resistance at the variable resistor's position in the voltage clamping circuit goes high, the voltage drop across the variable resistor position goes high.